feat: Use Bazel's Packaged Java (#24)

Add wrappers around Java and Bazel. `_java` now references bazel's
installed Java, and `_bazel` now adds startup options.

We suspect setting up Java adds additional startup flags, which incurs a
Bazel server start latency.

Future work may include allow passing in specific Bazel / Java / etc.
versions, which we can address if need be (config file? lots of input
variables? respecting .bazelrc-esque files?)

Suggested by @pat.

.github/workflows/compute_impacted_tests.yaml

@@ -11,12 +11,6 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v3
 
-      - name: Setup Java
-        uses: actions/setup-java@v3
-        with:
-          distribution: oracle
-          java-version: "17"
-
       - name: Setup Bazel
         # trunk-ignore(semgrep): Trust third-party `bazelbuild` GH Action
         uses: bazelbuild/setup-bazelisk@v2
@@ -30,7 +24,7 @@ jobs:
           PR_BRANCH: do_not_delete/stable_test_branch
           VERBOSE: 1
           WORKSPACE_PATH: ./tests/simple_bazel_workspace
-          BAZEL_STARTUP_OPTIONS: --host_jvm_args=-Xmx12G,--block_for_lock
+          BAZEL_STARTUP_OPTIONS: --host_jvm_args=-Xmx12G,--block_for_lock,--client_debug
 
       - name: Validate Impacted Targets Computation
         shell: bash

action.yaml

@@ -29,12 +29,6 @@ inputs:
 runs:
   using: composite
   steps:
-    - name: Setup Java
-      uses: actions/setup-java@v3
-      with:
-        distribution: oracle
-        java-version: "17"
-
     - name: Setup Bazel
       # trunk-ignore(semgrep): Trust third-party `bazelbuild` GH Action
       uses: bazelbuild/setup-bazelisk@v2

src/scripts/compute_impacted_targets.sh

@@ -1,6 +1,7 @@
 #!/usr/bin/env bash
 
 set -euo pipefail
+shopt -s expand_aliases
 
 if [[ (-z ${MERGE_INSTANCE_BRANCH}) || (-z ${PR_BRANCH}) ]]; then
 	echo "Missing branch"
@@ -30,11 +31,19 @@ if [[ -n ${BAZEL_STARTUP_OPTIONS} ]]; then
 fi
 logIfVerbose "Bazel startup options" "${bazel_startup_options}"
 
+_bazel() {
+	# trunk-ignore(shellcheck)
+	bazel ${bazel_startup_options} "$@"
+}
+
+# trunk-ignore(shellcheck)
+alias _java=$(_bazel info java-home)/bin/java
+
 bazelDiff() {
 	if [[ -n ${VERBOSE} ]]; then
-		java -jar bazel-diff.jar "$@" --verbose
+		_java -jar bazel-diff.jar "$@" --verbose
 	else
-		java -jar bazel-diff.jar "$@"
+		_java -jar bazel-diff.jar "$@"
 	fi
 }
 
@@ -81,9 +90,8 @@ fi
 
 # Install the bazel-diff JAR. Avoid cloning the repo, as there will be conflicting WORKSPACES.
 curl --retry 5 -Lo bazel-diff.jar https://github.com/Tinder/bazel-diff/releases/latest/download/bazel-diff_deploy.jar
-java -jar bazel-diff.jar -V
-# trunk-ignore(shellcheck/SC2086)
-bazel ${bazel_startup_options} version
+_java -jar bazel-diff.jar -V
+bazel version # Does not require running with startup options.
 
 # Output Files
 merge_instance_branch_out=./${merge_instance_branch_head_sha}